1. Field of the Invention
The present invention relates to a method for correcting a control of an optical scanner and an optical scanner.
2. Description of Related Art Including Information Disclosed Under 37 CFR §§1.97 and 37 CFR 1.98
Optical scanners, which are understood below to include in particular deflecting devices for controlled deflection of a beam of optical radiation that can be controlled in particular by preselecting a target movement or can be controlled by control signals, are used in various areas of technology. Laser scanning microscopes constitute an important area for use of such optical scanners. With laser scanning microscopes, a sample is scanned with a laser beam focused as a rule in a spot on a layer of the sample, whereby the focus is confocally mapped on a detection device. To deflect the laser beam to a predetermined position on the sample and to deflect the detection radiation emanating from the focus to the detection device, a deflection device, i.e., an optical scanner is used, permitting controlled deflection of the laser beam, i.e., the detection radiation. For detection of an image of a layer of the sample, the laser beam and/or its focus is guided line by line over the sample from a first end position to a second end position and then back, with the beam being deflected in each of the end positions in a direction orthogonal to the direction of movement in the line, so that the focus jumps to the next line. The focus is moved in the most linear and uniform possible movement in the line, so that by detection of the detection radiation in constant time intervals, a pixel representation of an image in which the pixels, which are also arranged in a matrix, are assigned to the locations, is obtained, in which the pixels are then also arranged in the form of a matrix so they are equidistant. Therefore, an undistorted image is obtained only when the movement of the focus corresponds precisely to a uniform linear movement. The requirements of accurate control of an optical scanner used in a laser scanning microscope are very high.
To obtain a high accuracy, as described in DE 197 02 752 C2 (U.S. Pat. No. 6,037,583), for example, by means of a position sensor, the position of the drive and/or the mirror of the scanner may be detected in the form of a feed-back signal and/or a position signal on the basis of which deviations from a target position are corrected. However, this procedure is not accurate enough for high scanning speeds. Electronic processing of feedback signals and detection signals leads to distortion of the signals and to phase differences between the signals. In addition, owing to deformation of the scanner wave by means of which the drive movement is transmitted to the mirror, and deformations in the scanner mirror itself, the reported position does not correspond to the actual position of the mirror. The actual position of the deflected beam thus does not correspond to the desired target position.
It is therefore possible to perform an optical calibration of the scanner in which the control of the scanner is adjusted so that the actual movement of the focus corresponds to the target movement as accurately as possible.
However, even when there is very good optical calibration, errors in the image, e.g., a “fraying” of vertical lines or distortion of the image geometry may occur after an extended period of time with a bidirectional scan due to wear on the scanner, in particular a drive unit of the scanner, because the scanner does not respond to control in the same way as in optical calibration. However, optical calibration is too complicated and expensive to be able to perform it frequently.